Inner and outer surface cladding of pipes and vessels and welding of such components create numerous inspection difficulties which the current nondestructive testing art does not satisfactorily surmount. The problem is not usually a lack of ultrasonic indications but rather the inability of conventional methods to discriminate against the false indications and productively use the true indications. Inner and outer stainless steel cladding defeat many test methods due to the clad-base metal interface creating multiple scatterers, the material inhomogeneity and anisotropy inherent in cladded components, the possibility of buried flaws, etc. Welds produce additional scatterers, interfaces, material inhomogenieties and buried flaws and often join other structures to the surface of the component which limit the inspector's access to either the right side or left side of the flaw and/or to the inside or outside surface of the component. Further, testing for underclad cracks which originate at the clad-base metal interface or near mid-wall in a pressure vessel present additional testing difficulties because these flaws are without a strongly reflective corner as is the case for a surface connected crack.
Unfortunately, these difficulties are often simultaneously present and synergistically combine to create inspection difficulties. Further, the very subjects of the above described inspection difficulties, i.e. welds and cladding are often the very source and location of cracks. These matters are of the greatest commercial importance as many of the difficult-to-inspect components are found in nuclear reactor vessels and coolant piping to nuclear reactor vessels.
These and other test difficulties currently existent in the nondestructive testing art are described in greater detail herein and in the above related applications. The prior art disclosed by the inventor and cited by the examiner in the above related applications is material to the current invention and is expressly incorporated herein.
Other material art includes Silk, M. G., Lidington, B. M., Montgomery, P., and Hammond, C. G., "Ultrasonic Time-Domain Measurements of the Depth of Crack-Like Defects in Ferritic and Austenitic Steels," in Proceedings of Specialist Meeting on the Ultrasonic Inspection of Reactor Components, Risley, England, September 1976; and Cook, R. V. Latimer, P. J., and McClung, R. W., "Flaw Measurement Using Ultrasonics in Thick Pressure Vessel Steel," Final Report on Contract No. W-7405-eng-26 prepared by Oak Ridge National Laboratory for the U.S. Nuclear Regulatory Commission, Oak Ridge, Tenn., August 1982.
Silk typifies the art's reliance upon only one type of wave mode in any given test, the art's preference for separated probes and its typical nonuse of the phenomena of mode conversion for flaw characterization. Specifically, Silk shows a transmitting transducer on a first shoe located on one side of the target area which beams an incident ultrasonic wave at the target area to produce a returning wave of the same mode received by a receiving transducer located on a second shoe located on the other side of the target area.